OP177

Data Sheet

Rev. H | Page 10 of 16

PRECISION HIGH GAIN DIFFERENTIAL AMPLIFIER

The high gain, gain linearity, CMRR, and low TCVOS of the

OP177 make it possible to obtain performance not previously

available in single stage, very high gain amplifier applications.

See Figure 28.

For best CMR,

R2

R1

must equal

R4

R3

In this example, with a 10 mV differential signal, the maximum

errors are listed in Table 6.

0.1µF

+15V

R1

1kΩ

R3

1kΩ

R2

1MΩ

0.1µF

–15V

R4

1MΩ

2

3

7

6

4

OP177

–

+

Figure 28. Precision High Gain Differential Amplifier

Table 6. High Gain Differential Amplifier Performance

Type

Amount

Common-Mode Voltage

0.1%/V

Gain Linearity, Worst Case

0.02%

TCVOS

0.0003%/°C

TCIOS

0.008%/°C

ISOLATING LARGE CAPACITIVE LOADS

The circuit shown in Figure 29 reduces maximum slew rate but

allows driving capacitive loads of any size without instability.

Because the 100 Ω resistor is inside the feedback loop, the effect

on output impedance is reduced to insignificance by the high

open loop gain of the OP177.

–

+

OP177

0.1µF

+15V

RS

RF

0.1µF

–15V

2

3

7

6

4

INPUT

100Ω

10pF

CLOAD

OUTPUT

Figure 29. Isolating Capacitive Loads

BILATERAL CURRENT SOURCE

The current sources shown in Figure 30 supply both positive

and negative currents into a grounded load.

Note that

R1

R3

R2

R4

R5

R2

R4

R

Z

O





















1

5

and that for ZO to be infinite

R1

R3

must

R2

R4

R5





PRECISION ABSOLUTE VALUE AMPLIFIER

The high gain and low TCVOS assure accurate operation with

inputs from microvolts to volts. In this circuit, the signal always

appears as a common-mode signal to the operational amplifiers

(for details, see Figure 31).

–

+

OP177

R1

100kΩ

R3

1kΩ

2

3

6

VIN

R2

100kΩ

R4

990Ω

R5

10Ω

IOUT ≤ 15mA

–

+

OP177

R1

R3

2

3

6

VIN

R2

R4

R5

IOUT ≤ 100mA

50Ω

+15V

–15V

2N2222

2N2907

IOUT = VIN

R3

R1 × R5

GIVEN R3 = R4 + R5, R1 = R2

BASIC CURRENT SOURCE

100mA CURRENT SOURCE

Figure 30. Bilateral Current Source